The invention relates to an aircraft fuselage, divided by an intermediate floor into an upper deck, preferably constructed as a passenger area, and a lower deck, constructed as a freight area, with a lower floor arranged in the lower deck, below which there is a bilge area, and with a ventilation installation with compressed air ducts through which fresh air can be fed into the upper deck which as exhaust air can be conducted from the upper deck via openings in the intermediate floor, preferably arranged in the area of the fuselage wall, into the lower deck and from there to the outside through one or more discharge valves.
The ventilation of the upper and lower decks to be carried out in an aircraft fuselage of the previously designated design is done under appreciable excess pressure compared with the ambient pressure and acts both as an air exchange and as heating. In typical aircraft fuselages there are large cross-sectional faces available for the cabin exhaust air in the lower floor areas. In spite of the drop in pressure on the flow path of the ventilation air, this results in low flow speeds in the lower deck. Because of the extremely low outside temperature in the largely predominating operating area of aircraft, appreciable temperature gradients occur owing to the lack of additional heating in the lower deck of aircraft, as a consequence of which considerable lifting forces act on the ventilation air. The flow speeds achieved in the openings in the intermediate floor owing to the drop in pressure or the pulse resulting therefrom are not sufficient, compared with the lifting forces, to avoid marked layer formation of cold and warm air in the lower deck. This may give rise to impermissibly cold areas in the lower deck.